Eyepiece.



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PATNTED MAY 14, 1901. H. c, LOMB.

EYEPIEGE.

APPLIUATIGN FILED IBB, 11, lo?.

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Y @my Lf/M mams Pmsns mc Liwcwismnmx c UNITED STATES PATENT OFFICE.

HENRY C. LOMB; OF ROCHESTER, NEW YORK,` ASSIGNOR To RAUSCH AND LOMR OPTICAL COMPANY, or ROCHESTER, NEW YORK, A CORPORA- ITioN or NEW YORK.

EYEPIECE.

Specification of Letters Patent.

'Patented May 14, 1907.

Application ned rebmry 11,1907. semi No. 356,812. A

To all whom it mor/g; con/cern,.-

`fie it known rthat l, HENRY C. LOMB, a citizen of the United States, residing at i Rochester, in the county of Monroe, State drawing.

This invention relates to optical instruments, and more particularly to an improved eyepiece for such instruments, and the principal or basic object of the invention is to provide an eyepiece `or eyepiece System which has a focal or working distance greater than the equivalent focal length thereof.

In an astronomical telescope, field glass and similar instruments the image formed by the objective is viewed and magnified by the eyepiece, the objective and veyepiece. being so placed relatively to each other that the posterior focus Ofdthe former coincides with the anterior focus Of the latter, and this anterior focus is situated very near to the eyepiece or actually in the interior thereof. ln the latter case, the eyepiece is as a matter of course useless for i'i'ieasuring instruments where cross hairs or lines must be employed, preferably,'for accuracy iny the focus of the objective of the instrument. In the case of' the location of the anterior focus of the eyepiecenear to and slightly in advance of the collective lens of the eyepiece dust or foreign matter will be-seen simultaneously with the image which is annoying and materially contributes to inaccuracy in measurements- In certain forms of telescopes, field glasses and other optical instruments the image formed by the obiective `or objective system is at a considerable distance from the eyepiece, so much so that it is quite inaccessible. That is to say, the objective image cannot be focused with the eyepieces now in use by reason of the distant location of the image. This occurs, for example, in the case of a reversing system composed of tically virtual and is situated. in' the interior ofthe prisms.

The problem involved in my present invention is, in brief, to discover orprovide a form of eyepiece whose anterior focus lies at a very considerable distance from its colof the eye may lective so that it can work through the prisms, when used, or a portion of them.

To take the problem in the most general way, inquiry is made in regard to the laws governing the combination of two lenses of focal lengths f, andf2 respectively, placed at a distance d apart, the resulting `system to have a prescribed equivalent focal length f and a prescribed focal or working distance wA It may be shown that the separation d of the lenses must be d 2 (l-Q-U) From y this equation it follows that if the working distance w is to be greater than f, f2 must be composed of two lenses or lens systems of focal length f, and j', respectively must have for its second element a lens of negative focal length and Separated from the other elements or lenses 'by a certain distance d defined by the above equation to give a working distance w. longer than the e uivalent focal length of the entire system. erein lies the novelty of my form and'construction of eyepiece. In addition tothe above the focal lengths and separation of the combination of lenses of such an eyepiece are such that vthe exit pupil or eye-point of the complete-system is so situated that the upil be brought into coincidhnce with it. v

Other objects and advantages of the invention will be set forth in the following descriptin and the novel fea-turesthereof will be particularly pointed out in the claims.

vIn, the drawing :Figure 1. is a diagrammatic illustration of an eyepiece constructed in accordance with my invention; Fig. 2 is a diagrammatic representation of the principal elements of a telescope rovided with my improved'eyepiece, and Fig. 3 is4 one of many modifications which may be employed in the elements of .my improved eyepiece andI their relative arrangement.

Like letters refer to like parts in the several l ,figures of the drawing. prisms in which the erected image is prac- A, Fig. 2, represents the objective of an optical instrument. B the collective and C the eyelens of an eyepiece constructed in accordance with my invention and relatively arrangedwith each other and as a whole with the objective' of the telescope.

vFor a clear understanding of the relative negative; whence it follows that an eyepiece i arrangement and individual characteristics of the elementsof my eyepiece which is constructed in :accordance with the formula above given reference is made to Fig. 1 wherein C -is 'a negative lens, B the ositive collective lens of the eyepiece and is the exit pupil of 'the instrument. -function of the lenses mentioned when given the proper separation is to produce 4the-Workro ing distance w,` which is greater than the equivalentfocal length of thesystem. From this arrangement and relation yof the two elements of the eyepiece flow heretofore specified.

It is, ofcourse, understood that the elementsy of the eyepiece may be modified in lines appearing distinctly .thereon whereby arrow and it iis in' theplane of this image' that the cross-hairs orlines arelocated, and

the workingdis'tanee-v-of thee epiece shown extends to the sameyplalxegan consequently e with the' cross hairs or acturate measrementsc anbe accomplished.

'. It will also be uotedlth'at. the exit pupil of the instrument is `exterior tothe eyepiece and 'at a considerable distance'v therefrom s'o -that the eye of the observer can be readily dplaced therein, and at a pointfwhere the light-is strongest and thus gives the greatest definition. By the construction and relative arrangement o f the principal elements' of the eyepiece hereinbefore described the longest pos- The optical the advantages from the former whereby afworkl sible working distance is secured and one which is longer than the equivalent focal length of the 'entire eyepiece.- ,The focal length of the eyepiece system is the distance between the posterior principal focus and the nodalpoint of emergence, or'tne distance between the anterior principal focus and the corresponding nodal point. The back focus has been designated as focal distance or working distance.

Havlng nowdescrlbed my inventlon and 4set forth its meritswhat l claim and-desire to secure by Letters Patent is .1. An eyepiece comprising two lenses one of which has a negative focal length and sepa-l rated fro'm the other to ive .a Working distance longer than the equivalent focal length.

of the 'entire system.

2. An eyepiece comprising component lenses the equivalent focal length and separation of which such as to brin 'the exit lpupil or eyepointthreof to' suc a plane that the pupil of the A'eye of the observer may be brought into coincidence therewith.-

3. An eyepiece comprisin .two lpositive vlenses and a negative lens,;t eflatterbein the veyelens'of the eyepiecerandlse ,arate l i distance is produced longer'th'an theeqnivllent focal length of said lenses,` "j fk-The combination the objective of an optical'instrument, f eyepiece system comprisinga positive lcollective and a negative eyelens'separat'edifroin' each 'other to` produce' a' workingdistance longer than the,

equivalent focal length of said lenses.

In testimony whereof, I aflix my signature in presence of two'witnesses.v

p HENRY C. LOMB.' Witnessesz Gao. V. FLEcK'ENsTEIN. JAMES G. GREENE'. 1 I. 

